Polymer tube dry cooling tower

ABSTRACT

A polymer tube dry cooling tower designed to operate with internal fluid at or near atmospheric pressure.

FIELD OF THE INVENTION

This invention relates to heat exchangers.

BACKGROUND OF THE INVENTION

It is well known and common practice to use metallic heat exchangers for air-to-water heat exchange. These metallic heat exchangers can handle high internal pressures but are expensive to produce due to the cost of the raw material and methods of manufacture. Polymer heat exchangers are less expensive to produce and can handle moderate pressures, but can only be made with round tubes due to high pressures and thus are difficult to use with extended heat transfer surfaces like fins.

SUMMARY OF THE INVENTION

This invention serves to combine the cost effectiveness and corrosion resistance of polymer tubes (that are in contact with liquids) while allowing the integration of metallic fins. This requires use of a heat exchanger between the invention and cooled equipment, similar to the way an open cooling tower is used, but with water saving potential of dry cooling. More particularly, the present invention seeks to solve the cost and tube thickness/shape dilemma by creating a multi-tube corrugated channel heat exchanger that operates near atmospheric pressure. This reduces the tube thickness, increases heat transfer, and allows the placement of metallic fins to further increase heat transfer efficiency.

According to an embodiment of the invention, an air-to-liquid heat exchanger is constructed of polymer rectangular tubes with metallic fins between the tubes. Each end of the rectangular tube is connected on the liquid side to a header. One header serves as a liquid inlet and the other as a liquid outlet. The heat exchanger operates near atmospheric pressure, similar to an open cooling tower. Multiple heat exchangers are multiplexed into a frame with fans. Air is drawn through the heat exchangers by the fans to cool a liquid flowing through the heat exchangers.

Accordingly, there is provided according to the invention, an isolated and atmospheric pressure indirect heat exchange dry cooling tower for the cooling of water that has been heated in a different heat exchanger in which the water is used in an indirect heat exchange to cool a process fluid, the isolated and atmospheric pressure indirect heat exchange dry cooling tower including a rectangular housing; a fan placed adjacent said housing and configured to force or draw air through said housing; a tube bundle situated inside said rectangular housing; an expansion device in fluid communication with said tube bundle that is open to atmospheric pressure; wherein the tube bundle includes an inlet header, an outlet header, and a plurality of rectangular polymer tubes extending between and in fluid communication with the inlet and outlet headers.

DESCRIPTION OF THE DRAWINGS

The subsequent description of the preferred embodiments of the present invention refers to the attached drawings, wherein:

FIG. 1 is a representation of an open cooling tower system of the prior art.

FIG. 2 is a representation of a closed fluid cooler system of the prior art.

FIG. 3 is a representation of a dry cooling tower in an atmospheric pressure isolated system according to an embodiment of the invention.

FIG. 4 shows a coil bundle with rectangular polymer tubes according to an embodiment of the invention.

FIG. 5 shows multiple coil bundles multiplexed according to another embodiment of the invention.

FIG. 6 shows multiplexed coil bundles in an air conducting apparatus with fans according to a further embodiment of the invention.

FIG. 7 shows a coil bundle with aluminum fins between polymer tubes according to another embodiment of the invention.

FIG. 8 shows a coil bundle with no fins according to another embodiment of the invention.

FIG. 9 is a representation of a multi-channel tube according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an open cooling tower system. Open cooling tower 1 is connected to a thermal load 2, such as a building air conditioning chiller. Heat exchanger 3 separates the low pressure cooling tower piping loop 4 from the high pressure load loop 5 but allows heat transfer between the loops. Water leaving the heat exchanger 3 enters the open cooling tower 1 and is sprayed over fill 40 via water distribution system 41. The water collects in the cooling tower basin 7 which is open to atmosphere and allows for liquid volume expansion in loop 4. Pressurized expansion tank 6 allows for liquid volume expansion in loop 5.

FIG. 2 shows a closed fluid cooler system. Closed circuit fluid cooler 43 is directly connected to a thermal load 8, such as a building air conditioning chiller. Pressurized expansion tank 9 allows for liquid volume expansion in loop 10. No water is distributed over the heat exchange tube bundle inside closed circuit fluid cooler 42. Heat exchange is strictly with the air that is drawn or pushed through the tube bundle.

FIG. 3 shows an embodiment of the invention in an open/closed system, that is, a closed system that operates at atmospheric pressure. Polymer tube fluid cooler tower 11 is connected to a thermal load 12, such as a building air conditioning chiller. Heat exchanger 13 separates the low pressure fluid cooler piping loop 14 from the high pressure load loop 15 but allows heat transfer between the loops. Pressurized expansion tank 16 allows for liquid volume expansion in loop 15. Low pressure expansion tank 17 is open to atmosphere pressure and allows for liquid volume expansion in loop 14. Expansion tank 17 may have a membrane at the liquid surface to prevent evaporation and gas exchange with the atmosphere.

FIG. 4 shows a coil bundle with rectangular polymer tubes according to an embodiment of the invention. Rectangular polymer tubes 18 are connected between liquid inlet header 19 and liquid outlet header 20. Liquid inlet connection 21 and liquid outlet connection 22 permit fluid flow through the bundle. For the sake of reference, the tube bundle shown in FIG. 4 is approximately eight (8) feet in height, with rectangular tubes of approximately 5.5 inches in width making up approximately seven feet of the height, and each of the header tubes making up another six inches of the height. However tube bundles according to the invention may have a height of 4-10 ft for a double stacked unit as shown in FIG. 5. Bundles may be as tall as 30 ft for field-erected units. The width of the tubes preferably range from 2-12 inches in width, with an exemplary 5.5 inch tube shown in FIG. 9. The rectangular polymer tubes are preferably multi-channel tubes as shown in FIG. 9. The polymer tubes are preferably made from polyethylene or polypropylene, but may be optionally be made from any polymer material having a minimum tensile strength of 11 MPa between −30 to 70 degrees Celsius, elongation greater than 150%, minimum 0.5 GPa modulus of elasticity, and a water absorption less than 0.5%. The polymer tubes are preferably manufactured by extrusion or additive manufacturing, but may be made according to other process, such as thermoforming. Due to the fact that the fluid in the tubes is maintained at atmospheric pressure, the tube walls may be very thin, ranging from about 0.008 inches to about 0.20 inches in thickness, about 0.008 inches to about 0.015 inches in thickness, or about 0.008 to about 0.02 inches in thickness. The most preferred thickness is about 0.010 inch.

FIG. 5 shows multiple coil bundles multiplexed. Upper coil bundles 23 a-n are placed side by side. Lower coil bundles 24 a-n are placed side by side and below upper coil bundles 23 a-n. Inlet piping header 25 is connected to upper coil liquid inlet connections 26 a-n. Outlet piping header 27 is connected to lower coil liquid outlet connections 28 a-n. Crossover piping 29 a-n connect upper coil outlet connections 30 a-n to lower coil inlet connections 31 a-n.

FIG. 6 shows multiplexed coil bundles 23 a-n and 24 a-n in an air conducting apparatus 36 with fans 32. According to a preferred embodiment, apparatus 36 may be provided with an adiabatic assist, for example, wetted or moistened adiabatic pads (not shown) placed in the air intake pathway to passively cool the air entering the apparatus. Alternative, the air entering the apparatus 36 may be wetted directly with a spray assist system (not shown).

FIG. 7 shows a section of coil bundle with Aluminum fins 33 thermally affixed between rectangular polymer tubes 18. Fins provide increased thermal capacity and structural rigidity to increase internal pressure holding capability.

FIG. 8 shows a section of coil bundle with no fins between rectangular polymer tubes 18. Removing fins reduces thermal capacity and pressure holding capability but increases external corrosion resistance. 

1. A heat exchanger comprising: a plurality of rectangular polymer tubes in a parallel arrangement; said rectangular tubes connected at each end to fluid headers to form a coil bundle; at least one said coil bundle mounted into an air conducting box; the air conducting box fitted with a fan to move air across the coil bundle.
 2. The heat exchanger according to claim 1 wherein said coil bundle comprises a closed circuit system configured to operate at atmospheric pressure.
 3. The heat exchanger according to claim 1 further comprising aluminum fins affixed to the rectangular polymer tubes.
 4. The heat exchanger according to claim 1 arranged in a parallel path wet-dry cooling tower.
 5. The heat exchanger according to claim 1 further comprising an expansion device open to atmospheric pressure and in fluid communication with said plurality of rectangular polymer tubes.
 6. The heat exchanger according to claim 1, wherein said rectangular polymer tubes each constitute a single channel in an integrated multi-channel tube.
 7. The heat exchanger according to claim 1, wherein tube walls of said rectangular polymer tubes have a thickness of about 0.008 inches to about 0.20 inches.
 8. An isolated and atmospheric pressure indirect heat exchange dry cooling tower for the cooling of water that has been heated in a different heat exchanger in which the water is used in an indirect heat exchange to cool a process fluid, the isolated and atmospheric pressure indirect heat exchange dry cooling tower comprising: a rectangular housing; a fan placed adjacent said housing and configured to force or draw air through said housing; a tube bundle situated inside said rectangular housing; an expansion device in fluid communication with said tube bundle that is open to atmospheric pressure; said tube bundle comprising an inlet header, an outlet header, and a plurality of rectangular polymer tubes extending between and in fluid communication with said inlet and outlet headers.
 9. The isolated and atmospheric pressure indirect heat exchange dry cooling tower according to claim 8 further comprising aluminum fins affixed to the rectangular polymer tubes.
 10. The isolated and atmospheric pressure indirect heat exchange dry cooling tower according to claim 8, wherein said rectangular polymer tubes each constitute a single channel in an integrated multi-channel tube.
 11. The isolated and atmospheric pressure indirect heat exchange dry cooling tower according to claim 8, wherein tube walls of said rectangular polymer tubes have a thickness of about 0.008 inches to about 0.20 inches.
 12. A system for cooling a process fluid comprising: a first indirect heat exchanger configured to receive said process fluid from a cooling system such as a building HVAC system, data center cooling system, or other industrial cooling system, allow indirect heat exchange between said process fluid and a cooling liquid, and return cooled process fluid to said cooling system; a second indirect heat exchanger configured to receive said cooling liquid from said first heat exchanger, allow indirect heat exchange between said cooling liquid and atmospheric air, and return cooled cooling liquid to said first heat exchanger, wherein said second indirect heat exchanger comprises an isolated and atmospheric pressure indirect heat exchange dry cooling tower comprising: a rectangular housing; a fan placed adjacent said housing and configured to force or draw air through said housing; a tube bundle situated inside said rectangular housing; an expansion device in fluid communication with said tube bundle that is open to atmospheric pressure; said tube bundle comprising an inlet header, an outlet header, and a plurality of rectangular polymer tubes extending between and in fluid communication with said inlet and outlet headers.
 13. The system according to claim 12 wherein said coil bundle comprises a closed circuit system configured to operate at atmospheric pressure.
 14. The system according to claim 12 further comprising aluminum fins affixed to the rectangular polymer tubes.
 15. The system according to claim 12, wherein said rectangular polymer tubes each constitute a single channel in an integrated multi-channel tube.
 16. The system according to claim 12, wherein tube walls of said rectangular polymer tubes have a thickness of about 0.008 inches to about 0.20 inches. 